1. Field of the Invention
The present invention relates to an optical information recording/reproduction apparatus and, more particularly, to optical information recording/reproduction apparatus capable of recording a signal and simultaneously verifying the recorded signal, i.e., capable of executing a so-called direct verify operation.
2. Related Background Art
Since an information recording/reproduction apparatus using an optical information recording medium such as an optical disk generally has advantages such as a removable recording medium, a high density, a large capacity, and the like, it is utilized in various fields. In recent years, a magnetooptical recording/reproduction apparatus for magnetooptically recording/reproducing information onto/from a magnetooptical recording medium has received a lot of attention. Such an apparatus is put into practical applications, e.g., an external storage apparatus of a computer, a document file recording/reproduction apparatus, and the like since it can rewrite information. In magnetooptical recording apparatuses, in order to further increase the data throughput, extensive studies about an over-write method, a direct verify method, and a high-density recording method which can achieve both the two methods have been made.
Conventionally, various direct verify methods have been proposed. For example, as shown in FIG. 1, a method of sequentially scanning a first light spot 113 and a second light spot 114 on an information track 116 on a recording medium is known. More specifically, the preceding first light spot 113 records an information pit 115 corresponding to data to be recorded, and the next second light spot 114 reproduces the information pit 115 to check if information is correctly recorded. According to this direct verify method, since recording and verify of information can be performed in one revolution of an information recording disk, the data throughput can be greatly increased. However, in order to simultaneously perform recording and verify, two light spots are required. In order to form the two light spots, a method using a plurality of lasers as light sources, as disclosed in, e.g., Japanese Laid-Open Patent Application No. 52-3405 or U.S. Pat. No. 4,583,210, and a method using a semiconductor laser array as a light source, as proposed in U.S. Pat. No. 4,517,667 are known. In these conventional verify methods, after recorded data is fixed (a recording state is stabilized), it is detected if the recorded data is normally recorded.
Contrary to these methods, in recent years, for example, Japanese Laid-Open Patent Application No. 3-86955 proposes a method to be called a simplified pseudo direct verify method. This method will be briefly described below. FIG. 2 is a schematic diagram of a magnetooptical recording/reproduction apparatus described in Japanese Laid-Open Patent Application No. 3-86955. In this example, a single light beam modulated according to a recording signal is emitted from a semiconductor laser in an optical pickup 124. The light beam reflected by a magnetooptical disk 121 is received, and is compared with the recording signal by a comparator 125, thereby detecting whether or not data recording is normally performed.
However, in the conventional method of performing a verify operation using the two light spots, the construction of the optical head is complicated, and alignment between the two light beams requires a troublesome operation. When the two light spots are separated excessively away from each other, one light spot is deformed by an aberration generated due to insufficient performance outside the optical axis of an objective lens. For this reason, reproduced signal quality is degraded, and reliability of a verify operation is impaired. On the other hand, in the pseudo verify method using one beam, although the optical system has a simple construction, since unerased, i.e., previously recorded old information remains on a leading portion of the light spot, an information component to be written and a previously written old information component are mixed in a verify signal, thus impairing reliability of a verify operation.